Recrystallized Grain Size Research Articles

Numerical simulation and experimental verification of microstructure evolution in a 3-dimensional hot-upsetting process

A coupled thermoviscoplastic finite-element software has been developed for modeling metal flow in hot metal-forming processes, especially for predicting the microstructural changes and mechanical properties of the products. Using this code, the dynamic recrystallization kinetics and recrystallized grain-size distributions during hot metal-forming processes can be simulated. In order to confirm the validity of the code developed, the results of an experiment into 3-dimensional hot upsetting (45 steel) are reported in the present paper, the recrystallized grain sizes being found to be in good agreement with the simulated results.

Evolution of the Microstructure in the Processes of Hot Compression and Drawing-Rolling.

The paper deals with the problem of the prediction of the microstructure evolution during the hot deformation of carbon-manganese steels. The objective of the work is the validation of the approach which incorporates an advanced thermal-mechanical finite-element model with the conventional closed form equations describing processes of static recrystallization and grain growth. Two types of the experiments are performed. The first is a typical multistage hot compression test for the axisymmetrical samples. The second is hot drawing of the flat samples through a set of the roller dies. An influence of initial grain size, starting temperature, strains and interpass times is investigated. The results include validation of various equations describing austenite grain size and kinetics of static recrystallization for the carbon-manganese steels.

The development of discrete shear-zones in a granite: stress, strain and changes in deformation mechanisms

The development of millimetre-scale continuous shear zones in the Sidi Ali Bou Nab (Algeria) granite and their progressive transformation into discrete shear zones are presented. Increases in strain, stress and strain-rate magnitudes, as well as changes of deformation mechanisms are suggested by an evolution of the microstructure across these narrow shear zones. Temperatures are assumed to be constant. From boundaries to core, the most striking aspects of this evolution are: 1. (1) a decrease in the angle between the foliation and the shear zone 2. (2) a decrease in the recrystallized grain-size of quartz together with the development of a crystallographic orientation characterized by a strong concentration of c-axes around the Y-axis of the finite-strain ellipsoid 3. (3) the development of very-fine-grained feldspathic aggregates or layers, probably through dynamic recrystallization of original large crystals, and 4. (4) the replacement of original biotite by muscovite and a new generation of biotite. In the continuous shear zones the deformation is controlled by the behaviour of quartz. This mineral undergoes extensive dynamic recrystallization which probably favours a higher strain rate and a change in the active slip system from a dominant basal one in the outermost part of the structures, to a dominant prismatic one in its core. Paleopiezometry and strain computations show a shear strain up to 10 and an inferred steady-state differential stress to 100–130 MPa, respectively. The high stress level is suspect because the estimates are derived from recrystallized grain size which may be sensitive to strain and variations of chemical environment. Discrete shear zones develop in relation with dynamic recrystallization of feldspars in the core of continuous shear zones. Dynamic recrystallization of feldspars produces very-fine-grained aggregates (grain size of 6–7 μm) which coalesce and form a continuous layer at the central part of the shear zones. This fabric may result from 1. (1) a change in the driving flow mechanism from dislocation creep of quartz to dislocation creep or/and grain-boundary sliding of feldspar neoblasts, and 2. (2) a large strain softening that would favour strain concentration in the fine-grained matrix and the development of sharp shear-zone boundaries.

Stress dependence of recrystallized-grain and subgrain size in olivine

New experiments on Mt. Burnet dunite have been carried out to evaluate the effects of important physical parameters on recrystallized-grain size and subgrain size in olivine deforming under steady-state conditions. The experiments, done under both wet and dry conditions in a Griggs solid-pressure-medium apparatus, were conducted in constant strain rate, constant stress and stress relaxation modes at 10 kbar confining pressure, temperatures from 1000°C to 1300°C, strain rates from 10 −4 to 10 −8/sec and stress differences of from 0.5 to 10 kbar. For dunite deformed under wet conditions, recrystallized-grain size is slightly temperature-dependent but under dry conditions it is only stress-dependent with D = 137 σ −1.27 for D in μm and σ in kbar. Subgrain sizes also depend only on stress; for the dry experiments d = 28 σ −0.62 and for the wet ones d = 15 σ −0.69 . Subgrain sizes decrease with increasing stress but do not increase with decreasing stress and hence record only maximum stress levels. Recrystallized-grain sizes adjust to both increasing and decreasing stress levels, at minimal strains and times, and thus record the stress history. Because of this and of the inherent stability of recrystallized grains, this technique is regarded as more reliable than the subgrain size and free dislocation density and curvature methods for estimating stress magnitudes in tectonites having deformed in the steadystate.

Study on the grain size of annealed aluminium sheet (1st Report)

Grain size of recrystallization gives big effect ot surfacc roughening of deformed sheet and the surface roughness of products by means of cutting or plastic working is an important factor in quality control.The effect of grain size to the surface roughness of deformed aluminium sheet has been measured by use of kosaka-type surface flatness testing machine, and application of JIS specification of surface roughness to surface control of plastic working products has been discussed.The results of the study are summed up as follows.1. Relation between grain size and surface roughness of deformed sheet through deep drawing is in direct proportion.2. Effect of impurities to the surface roughness cannot be found at least in a tolerable range of measured error.3. The lowest limit of good surface in plastic working products should be about 4μ roughness. It is necessary, therefore, that specification of 6 S (3-6μ) in JIS is to be more in details.4. Perfect surface reguires 3 S (1.5-3μ) roughness and the necessary grain size for this purpose is more than 500 grains/mm2.5. A standard sample for roughness comparison was made for surface control of finished products of plastic working.

亜鉛の性状に及ぼす純度の影響について（第2報）高純亜鉛板の再結晶現象について

Recrystallization phenomena have been studied with 4 kinds of specimens (99%, 99.9%, 99.99%, 99.99%Zn). The results were as follows: (1) The higher the purity, the larger the grain size of primary recrystallization. (2) In 99.999%Zn, primary recrystallization is partially observed immediately after 10% cold-rolling, and is completed after 30% cold-rolling. (3) Secondary recrystallization occurs at a low temperature with increasing cold-rolling reduction. (4) At the same cold-rolling reduction rate, it was found that there exists a minimum point of secondary recrystallization temperature at 99.99% purity. (5) In recrystallization diagram of zinc specimens of higher purity than 99.9%, it was found that the grain size has the maximum value at a certain temperature.

Annealing of cold-worked aluminium (2nd report)

Annealing of cold-worked metals at proper temperatures produces recrystallization followed by recovery and growth of these recrystallized grains. They have the following characteristics:Recrystallization-(1) Nucleus boundaries appear around the places where recovery has been Perfect in a large block. (2) The heavier the working, the easier the recrystallization occurs. The size of nucleus becomes smaller, the number of it increases, and the size ratio of nucleus to sub-grain decreases with an increase in the rate of working. (3) The nucleus size in the lightly worked state is approximately equal to the sub-grain size, and that in the heavily worked state can grow up rapidly to the sub-boundary by the action of numerous polygonization walls. (4) At the beginning of recrystallization, the recrystallization boundaries lack in clearness. (5) The grain size of recrystallization is a unique function of the rate of working. (6) The higher the annealing temperature, the lower the value of micro-hardness immediately after the recrystallization. (7) There are no recrystallization nucleus in the metals cold-tensioned more lightly than 20%, but they are recovered by stress-induced migration of already existing boundaries. (8) At the beginning of recrystallization there is found a large local difference in micro-hardness and in strain-relief at etching pits in the heavily worked metals as well as in the lightly worked ones. (9) The banded structure is not subject to any prominent change from the recovered state, and it remains until the next coarsening stage.Growth of recrystallized grain, which was conventionally called "secondary recrystallization" or "coarsening", is customarily considered to occur after a certain incubation period. But, actually, the growth proceeds already in this period. Each recrystallization grain is an ordinary unit in this growth which depend mainly on the capillary tension of polygonization walls in respective grains, and each process is finished in a relatively short time.In this case, the growth of grain having a crystal plane near (100) on the specimen surface is prominent along the rolling direction, and that of grain having a crystal plane near (111) is prominent in the perpendicular direction. The frequency of a crystal plane near (111) on the specimen surface increases a little owing to this process.Thus, the duty of polygonization walls is important at the initial stage of this growth, but the analogous effect as seen in the ordinary grain growth become gradually prominent. When the grown-grain size reaches 10 or more times of average recrystallized grain size, the rate of growth increases rapidly by the effect of ordinary grain growth. This is the coarsening which takes place at first preferentially along the rolling direction.The original boundary in growth process mentioned above needs some time for its perfect disapperance after growth.To the above two stages of growth the auther, for convenience sake, has given names the "short range annexation" and "long range annexation" according to their mechanisms respectively.Lightly worked metals show quite different appearances because they have no short range annexation and have relatively large nuclei. Metals cold-tensined smaller than 20% go directly to the coarsening. The rate of these growths increases with the decrease of impurities.The results mentioned above will be discussed theoretically in the 3rd report.

Effect of Recrystallized Grain Size on Grain Growth

Effect of Recrystallized Grain Size on Grain Growth